This invention relates to a failsafe mechanism for rapidly returning a switch to an off position in the event the switch actuator fails when the switch is in an open position.
The term switch, as herein used, means any type of device that reciprocates between a first closed position and a second open position. An example of such a switch is a valve stem that closes the valve when in a first position and opens the valve when the stem is moved to a second position. Many valves are placed in generally inaccessible locations and are remotely positioned through a central control station. Electrically controlled linear actuators are typically connected to the stem of valves that operate to control the flow of fluids (liquid, gas or vapor) through the system. In the event of a power failure or a system failure, it is highly desirous to rapidly close all of the valves in the system to shut the system down and thus prevent damage from occurring. To this end, many spring loaded devices have been developed that act upon the valve to automatically close the valve when either the actuator fails or a shut down signal is sent to the actuator.
Although many of these spring equipped failsafe devices work well in practice, it has long been a problem to quickly and safely mount or dismount the device upon a valve because of the typically high spring forces involved. The inability to contain the spring in a compressed state can create a potentially dangerous situation.